The present invention relates generally to tape drives, and more particularly to magnetic tape head positioning apparatus for fine positioning of a multiple channel magnetic tape head in a closed loop magnetic tape head positioning system.
Tape drives are commonly utilized as secondary storage devices for back up of the primary storage devices such as disk drives utilized in large computers such as main frames and in small computers such as personal computers. For small computers, tape drives using quarter-inch cartridges (i.e., the width of the tape is nominally one-quarter inch) are widely utilized, since they are relatively small and provide sufficient storage capacities.
An important factor that determines the storage capacity of a tape utilized with a non-rotating magnetic tape head is the number of parallel, longitudinally oriented tracks utilized to record data. In other words, all other factors being the same, more tracks provide more storage capacity. The writing and reading of parallel tracks is achieved by magnetic tape head positioning apparatus for positioning the magnetic tape head at different locations in the transverse direction relative to the tape and its direction of travel.
Typically, the magnetic tape head positioning apparatus includes a stepper motor, an externally threaded lead screw driven by the stepper motor, and a head carriage assembly which supports the magnetic tape head and is driven by the lead screw along a path transverse to the tape travel direction. For writing and reading, the magnetic tape head is positioned at a location transverse to the tape movement axis as determined by the calibration of the particular tape drive for unformatted tapes, or as close to the center of a track as defined by servo information in a pre-formatted tape. In either event, the magnetic tape head would be positioned at one of the incremental locations defined by the stepper motor. Due to manufacturing variations in the tape drive and the tape cartridge, the magnetic tape head might not be positioned at the location wherein the read or write elements of the tape head are centered on the track or tracks being accessed.
The consequences of imprecise magnetic tape head positioning include distortion and low signal amplitude upon playback on a drive different from the one that wrote a tape, or even the inability to read a tape written by another drive. Further, magnetic tape head positioning apparatus that is not capable of precise head positioning places limitations on track density.